The present invention generally relates to the measurement of tire uniformity with a tire uniformity machine, and more specifically to an improvement in prediction made possible by the removal of machine contributions to the measurement data.
In the art of manufacturing pneumatic tires, rubber flow in the tire mold or minor differences in the dimensions of the belts, beads, liners, treads, plies of rubberized cords, etc., sometimes cause non-uniformities in the completed tire. Non-uniformities of sufficient amplitude will cause force variations on a road surface against which the tires roll, producing vibration and noise. When such variations exceed an acceptable maximum level, the ride and handling of a vehicle utilizing such tires will be adversely affected.
Tire uniformity machines are used to monitor the quality of the tire production process and may guide or incorporate corrective measures such as grinding to improve the balance and uniformity of a tire. In general, a tire uniformity machine subjects a tire to normal conditions of mounting, pressurization, rotation and load while collecting measurement data on variations of deflection, forces, moments, and velocity. A tire uniformity machine typically includes an assembly for rotating a tire against the surface of a rotating loading wheel. In this testing arrangement, the loading wheel is moved in a manner dependent on the forces exerted by the rotating tire and those forces are measured by appropriately placed measuring devices. When a tire being tested yields unacceptable results, shoulder and/or center rib grinders are used to remove a small amount of the tire tread at precisely the location of the non-uniformities detected by the measuring devices. In a sophisticated tire uniformity machine, the measurements are stored and interpreted in digital form by a computer, and rubber is removed from the tire tread using grinders controlled by the computer. Examples of machines utilizing these methods are disclosed in U.S. Pat. Nos. 3,739,533; 3,946,527; 4,914,869 and 5,263,284.
Unavoidably, tire uniformity machines are not themselves perfectly uniform, and tire uniformity measurement signals may include an erroneous contribution from the tire uniformity machine itself. In effect, minor variations in the design, construction and operation of a tire uniformity machine contribute to variations of deflection, forces, moment or velocity, which contaminate the tire uniformity measurements with a machine contribution.
As noted by U.S. Pat. No. 4,404,848 (""848), it is often the case that measured values contain errors due to rotation deflections of the rims that grip the inspected tire and/or the load wheel of the tire uniformity machine. In addition, small deflections occur due to the deterioration of parts, for example, by rust or by bruises that occur during use of the inspecting machines. A method to correct these types of errors is disclosed by the ""848 patent wherein the radial runout of the load wheel is measured without a tire in place, to obtain an erroneous deflection signal. The erroneous deflection signal is then multiplied by the spring constant of the measured tire and subtracted from the measured value of the radial force obtained from the tested tire.
U.S. Pat. No. 4,404,849 describes a method for correcting errors of measurement due to variations in tire pressure in a tire uniformity inspecting operation.
U.S. Pat. No. 5,614,676 (""676) describes a method of vibration analysis for tire uniformity machines by using signals from load cells when the machine idles. The signals are sent to a computer that outputs an alarm signal when the amplitude of vibration at selected frequencies exceeds acceptable levels.
U.S. Pat. No. 6,257,956, incorporated herein by reference, teaches a method for correcting errors of measurement made on tire uniformity machines by identifying and removing machine contributions from tire uniformity measurements. The method of the patent includes calculating the effect of the average machine contribution to the measured values of production tire uniformity as measured by a tire uniformity machine. The machine contribution signal is subtracted from the production tire measurement signals to provide a more accurate basis to evaluate the uniformity of a production tire and guide, as necessary, corrective measures. The method primarily includes the steps of performing one or more tire uniformity measurements on a test tire, and storing the average test tire uniformity measurement data to use as an indicator of the average machine contribution to tire uniformity measurements. When a production tire is measured on the same tire uniformity machine, the stored machine contribution data/signal is subtracted from the production tire data/signal to produce a corrected production tire uniformity measurement.
U.S. Pat. No. 5,396,438 (K. L. Oblizajek, assigned to General Motors Corporation), incorporated in its entirety by reference herein, discloses a method of manufacturing tires which preferably includes measurement of two or more low speed tire parameters, by determining transfer functions which are used to calculate predicted highway speed (high speed) force variations, and then comparing high speed values predicted for production tires to predetermined criteria for controlling manufacture of the production tires.
As described in application Ser. No. 09/817,983 filed Mar. 27, 2001, incorporated herein by reference, during the typical tire manufacturing process, factory floor measurements of tire uniformity are performed on tire uniformity machines (xe2x80x9cTUMsxe2x80x9d) which are used to monitor the quality of the tire production process and may guide or incorporate corrective measures such as grinding to improve the balance and uniformity of a tire. A factory floor TUM is a low speed unit, typically operated at 60 rpm (revolutions per minute) which corresponds to less than 10 Kph for a typical passenger car tire. The low speed TUM is also known in the industry as a xe2x80x9clow speed uniformity machinexe2x80x9d or xe2x80x9cLSUxe2x80x9d. As the tire is rotated, it is measured and ground simultaneously. In a sophisticated, low speed production tire uniformity machine, such as a Model No. D70LTX available from the Akron Standard Co. of Akron Ohio, the force measurements are interpreted by a computer and rubber is removed from the tire tread using grinders controlled by the computer.
Once a tire undergoes correction for force variations in a TUM, it is common manufacturing practice to remove the tire from the TUM and place the tire in a balance machine to measure the amount of imbalance of the tire. Typically, the tires are mounted in the balance machine in a manner similar to that of the tire uniformity machine and inflated to a preset pressure. The static (single-plane) and couple (two-plane) imbalances are measured by one of a variety of well-known methods. When a tire is found to be imbalanced to an unacceptable level, the tire is scrapped.
In the art, forces on a tire which is rolling under load on a load bearing surface are commonly broken down into three orthogonal components which will be primarily referred to herein as: radial, lateral, and tangential. Radial forces act in the tire""s radial direction, i.e., perpendicular to the tire""s axis of rotation. Radial forces are strongest in the vertical direction (e.g., wheel xe2x80x9chopxe2x80x9d) as the tire interacts with the load bearing surface, but may also have a horizontal (fore-aft, or xe2x80x9csurgexe2x80x9d) component due to, for example, the radial centrifugal force of a net mass imbalance in the rotating tire. Lateral forces act in a direction parallel to the tire""s axis of rotation, and generally occur where the tire""s surface touches the load-bearing surface. Lateral force causes either tire wobble or a constant steering force. Tangential or fore-aft force is experienced at the surface of contact between the tire and the load bearing surface in a direction both tangential to the tire""s outer circumference (e.g., tread surface) and perpendicular to the tire""s axis of rotation (thus also perpendicular to the radial and lateral forces). Tangential force variations are experienced as a xe2x80x9cpush-pullxe2x80x9d effect on a tire, which can be analogized to the sensation of a wheel barrow traveling over a bump in the road, i.e. increased force as the wheel barrow is pushed up the bump, and decreased force as the wheel barrow travels down the bump.
Of the three types of force (radial, tangential and lateral), tangential force variation (TFV) is the most speed dependent, and practically cannot be measured on a typical production low speed tire uniformity machine, which operates at a speed such as 60 rpm. Tangential force variation can only be effectively measured at highway speeds using a high speed, laboratory tire uniformity machine, such as a Model HSU-1064, available from the Akron Standard Co. of Akron Ohio. The high speed TUM is also known in the industry as a xe2x80x9chigh speed uniformity machinexe2x80x9d or xe2x80x9cHSUxe2x80x9d.
Since there are three orthogonal forces being considered, there are three separate force variation signals: radial force variation (RFV), lateral force variation (LFV), and tangential force variation (TFV). Fourier transformations of each of the three force variation signals will produce families of harmonic components (some of which may have a zero magnitude) for each of the three signals. The first harmonic of radial force variation can be abbreviated as xe2x80x9cR1Hxe2x80x9d for Radial 1st Harmonic; the first harmonic of lateral force variation can be abbreviated as xe2x80x9cL1Hxe2x80x9d for Lateral 1st Harmonic; and the first harmonic of tangential force variation can be abbreviated as xe2x80x9cT1Hxe2x80x9d for Tangential 1st Harmonic. Similarly, second harmonic components can be abbreviated as R2H, L2H, and T2H, for radial, lateral and tangential 2nd harmonics, respectively; and so on for third and higher harmonics of the three force variations.
U.S. Pat. No. 6,065,331 (K. Fukasawa, assigned to Bridgestone Corporation), incorporated in its entirety by reference herein, discloses a method and apparatus for predicting a higher-order component (2nd and higher harmonics) of high speed uniformity of a tire, and a method of manufacturing tires utilizing the method and apparatus. The method preferably comprises measuring, for a single tire within a tire lot, a low-speed dynamic stiffness at a frequency corresponding to a higher-order component to be predicted when the tire rolls at a low speed, and a high-speed dynamic stiffness at a frequency corresponding to the order when the tire rolls at a high speed, and then using the dynamic stiffness measurements in an Formula to predict high speed RFV or TFV from low speed measurements of RFV and effective rolling radius variation.
U.S. application Ser. No. 09/817,983 teaches a method for predicting a harmonic component of force variation comprising the steps of: collecting a first set of measurement data for a tire on a factory floor balance checker, and on a factory floor tire uniformity machine which is operated at a first speed; collecting a second set of measurement data for the tire on a test lab tire uniformity machine which is operated at a second speed higher than the first speed; determining transfer functions from the first set of measurement data and the second set of measurement data; collecting a third set of measurement data for a production tire on a factory floor balance checker and on a factory floor tire uniformity machine; and predicting the harmonic component of force variation for the production tire rotating at a prediction speed by applying the transfer functions to the third set of measurement data.
The method further comprises the step of collecting, as part of the first set of measurement data, data on a factory floor balance checker, which determines single plane balance in terms of single plane net imbalance mass and rotational angular location of the net imbalance mass. Alternatively, the method further comprises the step of collecting part of the first set of measurement data on a factory floor balance checker which determines two plane balance in terms of a net imbalance mass and rotational angular location of the net imbalance mass for each of two circumferential planes of the tire being balance checked.
The method further comprises the step of collecting the third set of measurement data for the production tire on the same factory floor balance checker and on the same factory floor tire uniformity machine as were used for collecting the first set of measurement data for the tire sample; and collecting the third set of measurement data while operating the factory floor tire uniformity machine at the first speed.
Although the method described in U.S. application Ser. No. 09/817,983 significantly improves the prediction for high speed uniformity, the prediction works better for some tire constructions than for others. In the conception of the invention, it was theorized that vibrations in the tire uniformity machine interact with certain tire constructions more than others, to cause errors in the predictions for those certain constructions.
xe2x80x9cAxialxe2x80x9d and xe2x80x9cAxiallyxe2x80x9d means the lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cCircumferentialxe2x80x9d most often means circular lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction; it can also refer to the direction of the sets of adjacent circular curves whose radii define the axial curvature of the tread, as viewed in cross section.
xe2x80x9cCyclical dataxe2x80x9d means data having repeating characteristics with a regular periodic frequency or time interval.
xe2x80x9cLateralxe2x80x9d means a direction going from one sidewall of the tire towards the other sidewall of the tire, generally across the tread perpendicular to the tire circumference.
xe2x80x9cPlyxe2x80x9d means a cord-reinforced layer of rubber coated radially deployed or otherwise parallel cords.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d mean directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cTangentialxe2x80x9d and xe2x80x9cTangentiallyxe2x80x9d refer to segments of circular curves that intersect at a point through which can be drawn a single line that is mutually tangential to both circular segments.
xe2x80x9cTread,xe2x80x9d means the ground contacting portion of a tire.
A method for predicting product performance using sample data from a manufactured product comprises the steps of (a) collecting first measurement data on a product sample at a first condition, (b) collecting second measurement data for the product sample at a second condition, (c) establishing transfer functions from the first measurement data and the second measurement data and simultaneously calculating a bias term representing test machine contributions to the data, (d) collecting third measurement data for product using the first condition, and (e) predicting the product""s performance for the second condition by applying the transfer function and bias term to the third measurement data.
In an illustrated embodiment, a method for predicting a harmonic component of force variation comprises the steps of collecting a first set of measurement data for a tire sample on a factory floor balance checker and on a factory floor tire uniformity machine which is operated at a first speed, collecting a second set of measurement data for the tire sample on a test lab tire uniformity machine which is operated at a second speed higher than the first speed, determining transfer functions and a bias term from the first set of measurement data and the second set of measurement data, collecting a third set of measurement data for a production tire on a factory floor balance checker and on a factory floor tire uniformity machine operating at the first speed, and predicting a harmonic component of force variation for a production tire rotating at a second speed by applying the transfer functions and bias term to the third set of measurement data.
The illustrated method is characterized by the step of selecting the tire sample as a sample set of one or more tires of the same construction which is substantially the same as the construction of the production tire for which prediction is desired, and by collecting the first set of measurement data on a factory floor balance checker which determines single plane balance in terms of single plane net imbalance mass and rotational angular location of the net imbalance mass.
Alternatively, the method is characterized by the step of collecting the first set of measurement data on a factory floor balance checker which determines two plane balance in terms of a net imbalance mass and rotational angular location of the net imbalance mass for each of two circumferential planes of the tire being balance checked.
In a specific embodiment, the method is characterized by the steps of collecting the third set of measurement data for the production tire on the same factory floor balance checker and on the same factory floor tire uniformity machine as were used collecting the first set of measurement data for the tire sample, and collecting the third set of measurement data while operating the factory floor tire uniformity machine at said first speed.
The invention also includes a method of correlating test data, measured on more than one machine, which includes measuring more than one set of data on the same sample of test articles under the same test conditions, calculating transfer functions and bias between the more than one set of data, and calculating the coefficient of determination R2 between a first set of test data and at least a second set of the data corrected by removing the bias term.
Additionally, the invention includes a method of tuning a test machine comprising using the bias between two sets of data measured on a highly precise master machine and the test machine as a measure of the precision of the test machine and adjusting the test machine until the bias level with respect to the master machine is within target parameters.
The invention further includes a method of diagnosing an imperfection in a test machine comprising analyzing changes in the bias term as correlated with changes in test speed wherein when the bias is growing in proportion to the square of the rotational velocity of the machine, then an unbalance exists in the machine, and wherein if bias is growing with speed in a linear fashion, there is a geometrical imperfection in the test machine.
It is an object of the invention to remove biases in the testing machine from calculation for prediction of product performance.
Other objects of the invention will be apparent from the following description and claims.